A conventional servo unit to remotely control a target object is normally provided with a motor-driven actuator as a servo mechanism. FIG. 7 shows an example of servo mechanism, wherein inner part of a housing box 10 being a substantially rectangular parallelepiped is depicted as a cross-sectional view.
Referring to FIG. 7, there are represented a small direct current (DC) motor 1 (hereinafter, briefly referred to as “motor”), a motor shaft 2 and an output shaft 3 of a servo, wherein a reduction gear shaft 4 for fitting a plurality of reduction gears therearound is installed intermediately between the motor shaft 2 and the output shaft 3. Although the detail description is omitted, rotational force of the motor 1 is transmitted to the output shaft 3 via a plurality of, e.g., four reduction gear sets connected to the motor shaft 2, the output shaft 3 and the reduction gear shaft 4.
A potentiometer 5 is installed at one end of the output shaft 3 within a housing box 10 to detect the rotation angle thereof. A servo system is configured so that rotation angle of the potentiometer 5 can be fed back to a corresponding circuit in a driving system, thereby controlling rotation angle of the output shaft 3. Reference numerals 6 and 7 represent a power supply cable and a driving circuit board respectively.
This kind of servo mechanism is normally used as a servo product to control a model plane, a ship, an automobile and so on. In this case, an output terminal plate (rotary flange) 8 to drive an arm functioning as an actuator is installed at the other end of the output shaft 3
Recently, there have been various attempts to render a robot to walk and to move like a human body by using such a servo system. Strong concern is focused on a human robot as one of new tastes of people (refer to a reference: Oho-mu company, 2004, A guide to make a two-legged walking robot for ROBO-ONE).
However, the conventional servo mechanism as described above is used as a single unit transmission shaft to control rotation angle of one shaft in one preset rotational direction. For example, there have been suggested no technology to obtain a servo unit capable of offering complex motions thereof which are necessary to control in two shafts directions.
The angle control of two shafts required for a joint motion of a robot can be achieved through configuration of robot servo mechanisms. For example, by constructing two sets of housing boxes having two servo mechanisms shown in FIG. 7, a servo mechanism of a robot can be provided so that the angle control for two shafts being crossed with each other becomes possible. For example, as shown in FIGS. 8A and 8B, two housing boxes such as servo mechanisms shown in FIG. 7 may be coupled by configuring robot servos so that the angle control in a crossed direction thereof becomes possible.
Specifically, there are depicted in FIG. 8A a first housing box 11 and a second housing box 12, each of housing boxes 11 and 12 functioning as a servo unit of a robot, wherein the housing boxes 11 and 12 are perpendicularly coupled to each other via a coupling plate 13. With this structure, the location (angle) of the first housing box 12 can be controlled through a first shaft 11a and at the same time the angle in a vertical direction thereof can be controlled through a second shaft 12a. As a result, joint motion of a robot can be controlled by employing these two robot servo units (i.e., the housing boxes 11 and 12)
In this case, however, size (dimension) of the joint should be large in view of shape of servo in order to construct a robot joint by coupling these servos. Further, the existence of coupling plate 13 to couple two servos makes the joint size larger. Accordingly, in a conventional robot joint servo, it is difficult to minimize the size of the servo system.
Meanwhile, referring to FIG. 8B, since two servo mechanisms described above (i.e., the housing boxes 11 and 12) are fixed by simply piling up one on another in 90°, size (dimension) of the servo system shown in FIG. 8B becomes smaller than that of the servo system shown in FIG. 8A. However, with the structure of the servo system shown in FIG. 8B, angle control for the shaft 11 a perpendicular to the ground and angle control for the horizontal shaft 12a are apart and deviated with each other in the vertical direction as shown in FIG. 8. Accordingly, control program to control motion thereof with a two-degree-of-freedom becomes complex; further, the operating program to drive a corresponding robot becomes complex. The joint motion also becomes unnatural.
In the description stated above referring to FIGS. 8A and 8B, for simplicity, description for frames necessary to configure a servo as a joint of a robot is omitted. From now on, a servo construction procedure employing frames will be described. First, the first housing box 11 composing a servo unit is inserted into a coupling frame 13A along a direction indicated by an arrow “A” and then fixed thereat, wherein the coupling frame 13A being bended in a “n” shape as depicted in FIG. 9. Then, the second housing box 12 which have been mounted and then fixed on a small frame 13B along a direction indicated by an arrow “B” is attached under the coupled frame 13A along a direction indicated by an arrow “C”. As a result, the first housing box 11 and the second housing box 12 are coupled as one body, thereby forming two rotational driving shafts 11a and 12a. Finally, a robot joint unit is configured.
However, as described referring to FIGS. 8A, 8B and 9, in a conventional robot joint unit constructing technique by coupling radio control type single shaft servos, dimension of the joint unit becomes larger when a robot joint unit is composed by using two shafts mechanism to accomplish a joint part of a robot while there entails an offset in two rotary output shafts if the joint unit becomes smaller.
There has been suggested a robot unit set capable of functioning as various robot joints, the robot unit set being configured by coupling a plurality of mechanisms with each other by means of joint members, wherein the robot unit set includes the mechanisms having a rotational driving shaft embedded therein along a right angle direction in a substantially cubic shaped housing box, respectively.
However, in order to accomplish this kind of robot unit set, embedded mechanism representing a two-degree-of-freedom should be installed in a single housing box. As a result, there entails considerable cost increase to develop such a robot unit set (see, e.g., international publication No. WO 2001/062448).